Abstract
INTRODUCTION: The COVID-19 pandemic disproportionately impacted the ageing population and persons with disability. Previous studies have used cross-sectional or descriptive designs, limiting the establishment of robust associations. Our objective was to examine prospective associations between functional disability and COVID-19 outcomes in ageing US adults. METHODS: This study included 9390 Health and Retirement Study participants from the 2018 wave, representing 64 044 633 adults aged 50 years or older, who completed the 2021 Pandemic Mail-in Survey. Baseline functional disability comprised activities of daily living (ADL) and instrumental ADL. COVID-19 outcomes included infection, emergency room utilisation, hospitalisation, length of hospital stay and post-COVID conditions (PCC). Multivariate regression and propensity-score weighting were applied to assess prospective associations between baseline functional disability, vaccination and COVID-19 outcomes. Targeted learning was applied to assess the association between functional disability and COVID-19 within each vaccination stratum. Mediation analysis was used to quantify the proportion of effects of functional disability on COVID-19 infection and PCC, mediated through vaccination. RESULTS: 1460 (16.2%) participants reported infection, 7985 (86.1%) were vaccinated and 178 (11.4%) of COVID-19 infected had PCC. Functional disability was associated with increased risk of infection (OR: 1.28, 95% CI 1.01 to 1.64) and PCC (OR: 2.24, 95% CI 1.05 to 4.47), while vaccination was protective against infection (OR: 0.53, 95% CI 0.42 to 0.67). Vaccination mediated a small portion of the effect of functional disability on infection and PCC, while showing no effect modification. CONCLUSIONS: Comprehensive strategies beyond vaccination are needed to decrease infections and prevent PCC for vulnerable ageing adults with functional disability. As the first study to prospectively investigate associations between functional disability, vaccination status and COVID-19 outcomes using nationally representative data, these findings provide a robust foundation for future research and policy decisions to protect vulnerable populations during public health emergencies.